Impregnated wood and process of treating wood



Patented June 24, 1930 JOSEPH R. COOLIDGE, 31), OF BROOKLINE,

I PATENT OFFICE MASSACHUSETTS, ns'srenon T MONTAN,

INCL, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTSIMPREGNATED WOOD AND PROCESS OF TREATING 'W OOD No Drawing.

This invention relates to the impregnation of wood with agents designedto render it resistant to fire or decay, or for the purpose of improvingthe characteristics of the wood in other respects.

' Thenatunal inflammability of wood, its susceptibility to decay and toattack by wood boring animalcule are serious objections to its use formany purposes. In order to m overcome these objections it is now acommon practice to impregnate wood with various materials depending uponthe properties which are to be imparted to'it. For example, it is ausual practice to impregnate Wood with creosote or toxic salts such aszinc chloride, copper sulphate, and the like, in order to render itresistant to decay. The impregnation of wood with certain salts toreduce its combustibility is also well known,

although not as widely practiced. Such salts as borax, ammoniumsulphate, ammonium chloride, and others, have been used exten sively forthis purpose, and a considerable number of salts which are commonly usedfor wood impregnation are valuable both for their fireproofingproperties and also as preservative agents. A very serious objection,however, to any impregnation with water soluble materials is the factthat the impregnating medium leaches rapidly from the wood when it isexposed to the weather. For example, shingles impregnated withfireproofing or preservative salts lose these agents very rapidly sothat in a relatively short time they are no better, from a practicalstandpoint, than shingles which have I not been treated. It has alsobeen found that when flooring and interior finish are impregnated withany of the common fireproofing 49 salts, such saltsabsorb moisture fromthe atmosphere in damp weather, notwithstanding the presence of finishcoatings of varnish, shellac, or the like, and the solutions resultingfrom such absorption frequently attack the finish, and in any eventleave discolored spots or streaks whichare highly objectionable from thestandpoint of appearance.

The present invention deals with this prob- 50 lem, and it aims todevise a thoroughly prac- Application filed June 3, 1927. Serial No.196,394.

tical method of impregnating wood to protect it either from fire, decay,or the like, which will eifectually overcome the objections abovedescribed.

Some of the more common fireproofing salts, such as ammonium chlorideand ammonium sulphate, depend for their fireproofing properties upon thefact that when heated to temperatures somewhat below the combustionpoint of the wood they give off non- 6o combustible vapors or gases.Other fireproofing salts, such as borax, lose their water ofcrystallization, or partially decompose at high temperatures, and thewater vapor or steam which results from such decomposition mixes withand dilutes the combustible gases created by the heating of the wood. Itis preferable to make use of both types of salts, and for this reason,and also from considerations of economy, it is preferable 7 to use boraxas one of the constituents of the impregnating medium. However, almostany impregnatiomin order to proceed ethciently, must be carried on atelevated temperatures, and if borax is present in the impregnatingsolution it produces a very ob jectionable discoloration of the wood.While this discoloration may be reduced materially by conducting theprocess at a lower temperature, this involves an increased treatingperiod and therefore a greater expense. Ac-

cordingly, it is 'a further object of this invention to prevent suchdiscoloration while still carrying onthe process at elevatedtemperatures. 5 Still another objection to the use of borax is the factthat if present in high concentrations it attacks the intercellularstructure of the wood .and weakens it materially. I have found, however,that this objection can be avoided by using ammonium chloride orammonium sulphate with the borax. A further advantage derived from thiscombination is that notwithstanding the fact that ammonium chloride andammonium sulphate are very corrosive and attack the linings of thecylinders of the treatin plants, and

even in the treated wood pro uce corrosion of the nails and metal partsin contact with it, still when either ammonium chloride or 1011 ammoniumsulphate is used with borax the objectionable features of both salts aresubstantially neutralized. Consequently, an impregnation with thiscombination of salts does not weaken the structure of the wood to anymaterial degree, and the corrosive action of the ammonium chloride orammonium sulphate is practically eliminated.

Considering first the problem of preventing discoloration of the wood, Ihave found after a long series of experiments that this objectionableaction can be avoided by using ammonium phosphate with the borax. Forfireproofing treatments satisfactory results can be produced by usingammonium chloride or ammonium sulphate (these two chemicals beingequivalents so far as this invention is concerned) borax, and ammoniumphosphate in approximately equal proportions.

However, I have further discovered that if common rock salt, or. sodiumchloride, is used with the above, or a similar mixture of fireproofingsalts, the penetration of the entire salt mixture is improved verysurprisingly. In other words, if a typical fireproofing treatment ismade with borax, ammonium chloride and ammonium phosphate, and a secondtreatment then is made under the same conditions with the same saltsplus a considerable percentage of rock salt, it will be found that avery much higher concentration of salts has been forced into the wood inthe second treatment than in the first. And this is true notwithstandingthe fact that the concentration of salts in the treating solution is thesame in both cases and that the same time, temperature and pressureconditions are maintained in making both treatments. This is a veryimportant advantage, especially when high concentrations of salts mustbe introduced into the wood. While this action may not be produced inall species of woods, it does occur in a large number of our commonspecies, such as white and red cedar, white and red oak, hemlock, andothers.

A further advantage attending the use of rock salt is that it reducesthe expense of the treatment. Both the borax and ammonium chloride arecheap, while the ammonium phosphate is too expensive to use alone, butthe rock salt is so much cheaper than any of the other ingredients, thatby using all four of these salts in approximate- 1y equal proportions,the expense of the mixture is brought down to very reasonable limits.

For fireproofing treatments a solution of from 20% to 40% of these saltsby weight in water is suitable. I prefer to make the solution by mixingthe salts in the proportion of one pound of salts to two pounds ofwater, and to force this solution into the wood at a fairly hightemperature, say for example, 180 to 200 F. Assuming that the wood undertreatment is dry red oak flooring, an entirely satisfactory impregnationmay be produced by forcing the solution into the wood at a temperatureof say 190 F. under two hundred pounds pressure for a period of from twoto three hours.

This impregnation should be performed in F. This results in introducinga high concentration of the salts in the wood.

It should be understoodthat the impregnation could be performed in otherways, and that the exact procedure adopted will necessarily depend uponthe equipment available, the kind of wood being treated,

the size of the pieces of wood under treatment, and various otherpractical considerations well understood by those skilled in this art.

The process above described produces a very complete impregnation of thewood, makes it highly resistant to fire, can be practiced economically,and avoids any objectionable discoloration of the wood. The wood sotreated is either air dried or kiln dried, as desired, and it is thenready for certain uses.

However, the process so far described deals simply with the problem ofdevising an effective and entirely practical method of rendering woodresistant to fire while avoiding discoloration and certain of the otherob ectionable features of prior practices. Vhile wood treated in thismanner is entirely satisfactory for some purposes, it would not besuitable for use in wet locations, or where exposed to the weather, forthe reason that the salts, being soluble in water, would leach from thewood and its resistance to fire thus would gradually be lessened. Afurther feature 0 this invention, therefore, deals with the sealing ofthese salts in the wood so that they will be protected from any harmfulaction of moisture.

The discovery of a material which will effectively hold the salts in thewood without, at the same time, reducing its fireproofing properties hasproved to be a very difficult matter. After a long series of experimentsI have discovered that an impregnation with ordinary soap satisfiesthese requirements.

In order to prepare the wood for this soap impregnation, it ispreferable to remove the excess water which has been forced into thewood during the impregnation above described with the salt solution.This may be done by removing the wood from the cylinder and allowing itto partially dry out, but preferably this object is accomplished bysubjecting the wood to a vacuum while it still remains in the treatingcylinder and immediately at the conclusion of the salt impregnation. Itis necessary to remove only about of the water which has been introducedin the first impregnating step, and whether this is done by air or kilndrying, or by subjecting the wood to a vacuum while still in thecylinder will depend largely upon conditions obtaining at the treatingplant.

According to this invention the wood which has previously beenimpregnated with salts is now impregnated with a solution of soap,ordinary laundry soap being satisfactory. A solution of one partordinary soap with five parts of water can be used with good results. Inview of the fact, however, that ordinary soap contains considerablewater, in some cases as high as 4.0%, it is preferable to use soap fromwhich the water has been practically eliminated, and a solution made bydissolving one part, by weight,

' of dry soap in ten parts of water is satisfactory. This impregnationis best performed in a pressure cylinder, the solution being kept hotat, say 150 F., and forced into the wood under a pressure of from 150 to200 pounds for a period of one hour. The temperature, pressure, and thelength of the treatment will be determined by the size of the piecesbeing treated and other practical considerations. The wood then isremoved from the cylinder and stacked where it can drain and dry out.

While the action which takes place in the wood is somewhat obscure, itseems clear that the impregnation with the fireproofing salts results inthe .deposit of these salts on and in the-walls of the pores andtracheids of the wood. The subsequent impregnation with soap results incoating the walls with this material, some of the soap solutionpreferably also entering the cell walls. A considerable part of thissoap apparently combines with ingredients in the salts and produces aninsoluble metallic soap. It may be also that some of the soap, eithersoluble or insoluble, plugs or seals the tracheids. In any event thesoap, does protect the water soluble salts from dissolving in moisturewhich is absorbed by the wood. The salts above mentioned are of theordinary commercial variety, as distinguished from the chemically puresalts, so that there are doubtless associated with them, as impuri-'ties, various metal salts which will combine with the soap to produce aninsoluble soap. Dyes also can be mixed with the treating 65 solution.

It is preferable, however, for most purposes not to rely on the presenceof such impurities to produce an insoluble soap in the wood, andconsequently, I prefer to mix with the salts which are used in makingthe first impregnation some salt, such as aluminum sulphate,-coppersulphate, or the like, which definitely will combine with the soapintroduced in the subsequent treatment to produce an insoluble metallicsoap. For this reason I prefer in making the fireproofing treatmentabove described to use with the borax, ammonium chloride, ammoniumphosphate and comomn salt, a proportion of aluminum sulphate equal toapproximately one-half the weight of the borax. While many salts otherthan aluminum sulphate could be used for this purpose, as will beobvious to those familiar with the manufac ture of insoluble soaps, Iprefer this particular salt because it is cheap and it combines with thesoap to make an excellent ofiicial tests prescribed by the city of NewYork. An extremely important advantage of wood fireproofed in thismanner is that it retains its fire resistant characteristicsindefinitely, even when exposed to the weather,

whereas wood treated by the comomn commercial processes gradualy losesits fireproofing salts when used out of doors or in damp locations. Avery important. practical advantage of this process is the fact that itcan be practiced in the ordinary commercial treating plants withoutrequiring any material change in equipment.

The fireproofing properties of the soap'may be further increased byadding to the soap solution a small proportion, say 25% of the weight ofthe soap, of some material such as aradichlorbenzene. Usually, however,this is not"necessary.

Wood treated as above described, in addition to being fireproofed, isalso highly resistant to decay. But it contains a much higherconcentration of salts than is neces sary simply to preserve it fromdecay. That is, .it may be necessary to add as much as nine or tenpounds of dry salts to a'cubic foot of wood of some species to protectit efi'ectually from fire, whereas a very much lower weight of saltswould be sufficient to preserve it from decay. Where, therefore, thefundamental object in treating the wood is to preserve it, the sameprocess above described can 'be followed and with the same salts,(although the ammonium chloride is not necessary) but the concentrationcan be reduced materially. Also, in making a preservative treatment theprocess may be somewhat simplified by stopping the first impregnationwhen a sufiicient quantity of the reservative has been forced into the wto give it the desired degree of toxicity. Assuming, for example, thatthe solution consists of borax, ammonium phosphate, and aluminumsulphate, and that the wood under treatment is dry red oak, the firststep could be stopped when the weight of the wood had been increased bya proximately The cylinder then shou d be washed out, some pressurebeing maintained during this washing 0 eration, and the soap solutionthen can be admitted to the cylinder and the second step of the processstarted atonce. A suflicient wei ht of the soap solution should beforced into the wood so that the dry weight of the soap introduced willbe about three times the dry weight of the aluminum sulphate. While thisprocess thus involves two steps or movements,-

it, uires but a single handlin of the wood, and the intermediate step ave de scribed of removin the excess water introduced in the firstimpregnation is avoided. While the borax is a ood toxic preservative, itcan be replaces by other preservatives, such as zinc chloride, coppersulphate, sodium fluoride, and others.

Man variations of the method above describe may be practiced within thescope of the invention. For exam 1e, under some circumstances it may besu cient simply to make an impregnation with insoluble soap, themetallic soap being formed in the wood by subjecting it to successiveimpregnations of salt and soluble-soap. Obviously the soluble soap alsocould be produced in the wood but this would involve additional expensewith no advantage.

Essentially the same process can also be used in protecting otherimpregating agents than those particularly mentioned. For example, woodcan be given an empty cell treatment with creosote and some of thedisagreeable features of the wood so treated. can be eliminated bysealing the creosote in with an insoluble metallic soap. Either thesoluble soap or the aluminum sulphate, or other salt which is to unitewith the soap, can be combined with the creosote in giving the firstimpregnation, a subsequent impregnation being made with the ingredientnecessary to act on the soap or salt to produce an insoluble soap.

In some cases, also, it may be referable to confine the impregnationwith t e insoluble soap to the outer strata of the wood where itsfunction as a sealing agentis more essential. In such cases the soapimpregnation can be made by the open tank process.

The methods above described can also be used to advantage in treatingwall board, fibre board, and the like, whichconsist chiefly or largelyof fibre of a woody nature, and they are particularly valuable infireproofing products of this character. Some of these wall boards orfibre boards have a relatively o 11 structure, as for example that knownas lotex, so that no impre ation problem is involved, while othersrequire substantially the same treatment as wood.

I have found it entirely possible. also, to mold articles of pulp orwood fibre. the fibre bein thoroughly moistened with aluminum sulphate,then to impregnate the molded article with a soap solution. When thisproduct dries out it is very firmly bonded to gether, is hard andstable, and is thereafter extremel resistant to the action of moisture.It shoul be understood therefore, that the term wood is used in t e apended claims, to include fibre articles 0 the character abovedescribed.

-It should also be understood that the, word impregnation is intended todesignate a treatment which penetrates the pores and tracheids of thewood for a substantial depth, as distinguished from a mere superficialtreatment or surface coating which probably never penetrates the woodfor a depth of more t an one sixty-fourth of an inch.

This application is a continuation in part of my pending applicationsSerial Nos. 155,- 766, filed December 18, 1926, and 181,276, filed April5, 1927, but the claims in this case are limited to subject matter notclaimed in said earlier applications.

Having this described my invention, what I desire to claim as new is:

1. An article of the character described comprising wood impregnated fora substantial depth with borax and ammonium phosphate.

2. An article of the character described comprising wood, the pores andcells of which for a substantial depth are impregnated with a mixture ofborax, ammonium chloride and ammonium phosphate.

3. That improvement in processes of treating wood which consists inimpregnating the wood at elevated temperatures with a solutioncontaining borax associated with a sufiicient quantity of ammoniumphosphate to prevent discoloration of the wood.

4. That improvement in processes of treating wood which consists inimpregnating the wood at elevated temperatures with a water solution ofborax, ammonium phosphate and ammonium chloride in substantialproportions.

5. That im rovement in processes of treating wood which consists inforcing into the pores and cells of the wood a hot watersolution ofprotective salts including borax v and ammonium phosphate, the solutionhaving a concentration of from 15% to 410%.

6. That improvement in processes of fireproofing wood, which consists inimpregnating the wood with water soluble fireproofing salts including asufficient percentage of common salt to promote the penetration of theentire solution.

7. That improvement in processes of treating wood which consists inimpregnating the wood at elevated temperatures with a water solution offireproofing salts including borax, ammonium phosphate and common salt.

8. That improvement in processes of treating wood which consists inimpregnating the wood at elevated temperatures with a water solution ofborax,- ammonium phosphate and ammonium chloride and sodium chloride. I

9. An article of the character described comprising wood, the pores andcells of which for a substantial depth are impregnated with a mixture ofborax, ammonium "chloride, ammonium phosphate and common salt.

JOSEPH R. COOLIDGE, III.

